This invention relates to a vehicle brake device which permits regenerative cooperative control, and particularly to a reliable and inexpensive vehicle brake device.
U.S. patent publication Ser. No. 2002/0140283A1 discloses a vehicle brake device which can perform regenerative cooperative control. One of the brake devices disclosed in this patent publication is shown in FIG. 4.
This brake device 10 includes a brake pedal 11, a hydraulic pressure generating device 12 for producing a predetermined hydraulic pressure by means of a power-driven pump, an electric control device 13 for controlling the brake device, a reservoir 14, a cylinder 15, a pressure adjusting valve 16, hydraulic passages 17, 20, 21, a master cylinder 18, an auxiliary hydraulic chamber 19 that receives the output hydraulic pressure of the pressure-adjusting valve 16, wheel cylinders 22–25 for imparting braking force to the vehicle wheels, electromagnetic proportional valves 26 and 27, pressure sensors 28 and 29, solenoid valves 28 and 29, and check valves 32 and 33.
In this brake device 10, hydraulic pressure P1 supplied from the hydraulic pressure generating device 12 is adjusted by the pressure adjusting valve 16 to a value P2 corresponding to the brake operating force applied to the brake pedal 11 and the hydraulic pressure thus adjusted is introduced into the auxiliary hydraulic chamber 19. The master cylinder 18 is activated by the introduced hydraulic pressure to generate hydraulic pressure P4 corresponding to the hydraulic pressure in the auxiliary hydraulic pressure chamber 19 in hydraulic chambers 18e and 18i of the master cylinder 18. The hydraulic pressure P4, which is output from the master cylinder 18, is supplied to the wheel cylinders 22–25, thereby producing braking force corresponding to the brake operating force.
For regenerative cooperative braking, a command is given from the electrical control device 13 to the electromagnetic proportional valves 26 and 27 to lower the hydraulic pressure in the auxiliary hydraulic chamber 19 from P2 to P3. By arranging such that the hydraulic pressure in the auxiliary hydraulic chamber 19 can be reduced to any value below the output hydraulic pressure of the pressure adjusting valve 16, the braking force produced under hydraulic pressure during regenerative cooperative braking can be reduced by an amount corresponding to the regenerative braking force, so that the regenerative braking force can be fully utilized for vehicle braking.
In the brake device of the JP patent publication 2002-264795, based on information from the pressure sensor 28, the electromagnetic proportional valves 26 and 27 are activated to control the hydraulic pressure in the auxiliary hydraulic chamber 19 to a given value below the output hydraulic pressure value of the pressure adjusting valve 16. Thus, if the pressure sensor 28 or electromagnetic proportional valves 26, 27 should fail during pressure adjustment, it is possible that the hydraulic pressure in the auxiliary hydraulic chamber 19 be reduced to 0 atm., so that the braking force may drop to zero.
An object of this invention is to solve this problem, thereby improving the reliability of a brake device used for regenerative braking.